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Chipotle has some foul words for McDonald’s. Though McDonald’s $50 million investment in Chipotle back in 1998 may have been instrumental in getting the burrito chain off the ground, Chipotle’s founder, Steve Ells, always sought to keep the fast-food giant at a reasonable distance.

And in some cases, it turns out, he was downright repulsed by McDonald’s practices. In a new profile by Bloomberg, Ells told his father that visiting a McDonald’s chicken farm in Arkansas was “absolutely the most disgusting thing he’d ever seen in his life.”

While Ells does not describe precisely what he saw on the farm, it ultimately fortified Chipotle’s vision of Food With Integrity -- which today includes sustainably raised, organic and locally-sourced ingredients whenever possible. “Up until that point it was about buying really good, fresh food,” Ells says. “But I had never visited the farms.”

Recently, Chipotle put its money where its mouth is when it stopped selling pork in 1,700 locations after finding a supplier had violated its animal-welfare standards.

At the same time, however, Chipotle execs acknowledge that a relationship with McDonald’s -- which represented the company’s first non-burger endeavor -- did bestow critical lessons in fields like distribution, real estate, construction, talent and organizational structures.

Now, how the tables have turned. Amid plummeting sales, McDonald’s is taking a page from Chipotle’s fast-casual playbook and emphasis on quality ingredients. In addition to tapping a new CEO, Steve Easterbrook, who has also served as chief of the fast-casual chains PizzaExpress and Wagamama, the company is slated to roll out a “Create Your Taste” platform featuring simplified recipes and localized ingredients.